1. Field of the Invention
The present invention relates to a method of an auxiliary tool used when a dentiform model is mounted on an occluding apparatus and a method of mounting the dentiform model on the occluding apparatus. Particularly, it relates to an auxiliary tool for an occluding apparatus which is suitable for production of a tooth positioner used in the final stage, for example, of orthodontic treatment and a method of mounting a dentiform model.
2. Prior Art
In clinical orthodontics, a tool referred to as a tooth positioner has been known as an apparatus used in the final stage of orthodontic treatment for attaining closer occlusion and slightly moving the teeth of a patient in cases such as a case where a relapse occurs in a short time after the orthodontic treatment. The tooth positioner is produced on the basis of a set-up model of the patient, which is made by separating teeth of a dentiform model made on the basis of an impression of the upper and lower Jaws of the patient as required and rearranging the separated teeth in an ideal set of teeth and in an ideal occluded state on the model.
The tooth positioner has a structure similar to a mouse piece (used in sports such as boxing), and is made of a material having elasticity and an original form restoring force, for example, rubber or silicon, so that an ideal set of teeth on the set-up model is carved thereon. When the tooth positioner is mounted in the mouth of the patient, the tooth positioner is first deformed by the difference between the actual set of teeth of the patient and the set of teeth on the set-up model which is carved in the tooth positioner. Thereafter, a continuous weak force is applied to the set of teeth during a mounting period by the original form restoring force of the tooth positioner, to finally move the teeth of the patient to an ideal position indicated by the set-up model. The use of the apparatus eliminates the necessity of using a complicated apparatus in the final stage of the orthodontic treatment, or makes it possible to shorten a period during which a complicated apparatus is mounted. In recent years, such usefulness has been reconsidered, so that the tooth positioner tends to be relatively often used.
FIG. 1 is a perspective view showing an example of a tooth positioner, and FIG. 2 illustrates the tooth positioner in a state where it is mounted in the mouth of a patient. An ideal set of teeth 2 on a set-up model is carved, as described above, in a tooth positioner 1. The set of teeth of the upper jaw 2 and a set of teeth of the lower jaw (not shown) are generally carved.
When the tooth positioner 1 is mounted in the mouth, the set of teeth 2 carved in the tooth positioner 1 and actual sets of teeth T.sub.U and T.sub.D of a patient are engaged with each other. However, after the tooth positioner 1 is deformed by the difference therebetween. A continuous weak force is applied to the actual sets of teeth T.sub.U and T.sub.D by an original form restoring force. The applied force is illustrated by + and - in FIG. 2.
In the tooth positioner 1, however, an occluded surface between the set of teeth of the upper Jaw T.sub.U and the set of teeth of the lower jaw T.sub.D (a surface where the upper and lower teeth are occluded) is covered with its material, so that the tooth positioner 1 is interposed between the upper and lower sets of teeth T.sub.U and T.sub.D (an area indicated by 3 in FIG. 2). That is, when the tooth positioner 1 is mounted, the upper jaw and the lower jaw are opened. Actually, the upper jaw is fixed to the head, so that the lower jaw is opened downward toward the back using the jaw joint as its axis.
The set-up model for the patient is made in a state where the respective sets of teeth of the upper jaw and the lower jaw are occluded. The reason for this is that the occluded surface and the size and the shape of the teeth differ from patient to patient, so that the arrangement of the teeth in an ideal occluded state cannot be presumed.
On the other hand, the tooth positioner is produced in a state where the set-up model made in the occluded state is opened by a suitable amount, that is, the upper and lower jaws are opened by the thickness of the tooth positioner to be interposed between the respective sets of teeth of the upper jaw and the lower jaw.
Consequently, the setting of a state where the jaws are moved when they are opened must conform to the anatomical and physiological functions in the jaw joints of the patient. Otherwise the respective sets of teeth of the upper and lower jaws would not be actually satisfactorily occluded, or would be occluded in an erroneous relationship between the upper and lower jaws after detaching the tooth positioner even if they are respectively regularly corrected by using the tooth positioner. As a result, the sets of teeth may be shifted immediately after the orthodontic treatment, and an excessive burden may be imposed on the jaw joints which correct the shift in the relationship between the upper and lower jaws for each bite. In either case, the mounting itself of a tool produced by unsuitably setting the relationship between the upper and lower jaws distorts the position of the lower jaw, thereby imposing a burden on the jaw joint.
In order to remove such harmful effects, an occluding apparatus and a side X-ray have been conventionally used in setting the amount of opening between the upper and lower jaws.
The occluding apparatus is an apparatus for connecting the upper jaw, the lower jaw and the dentiform model to one another, to reproduce the motion of the jaw joints of a human being. However, the apparatus is an apparatus for confirming a state where the sets of teeth are occluded, and the motion of the jaw joints is only reproduction of a certain degree of average motion. That is, the occluding apparatus has not been able to correctly reproduce the motion of the jaw joints for each patient.
Consequently, it is impossible to faithfully reproduce a state where the upper and lower jaws of each patient are opened by merely using the occluding apparatus.
A method using the side X-ray is a method of respectively tracing the set of teeth of the upper jaw and the set of teeth of the lower jaw on an X-ray of the face taken from just beside the face, opening the set of teeth of the lower jaw using the jaw joint as its axis, referring to the distance between the sets of teeth of the upper and lower jaws (a clearance) which occurs at that time, and setting the motion of the jaw joint. However, the method has the disadvantage in that it is almost impossible to clearly take an X-ray of the left and right jaw joints with they being exactly overlapped with each other. Even if the X-ray can be taken, the accuracy of the X-ray is not sufficient in that the motion in a three-dimensional manner of a state where the upper and lower jaws of the patient are opened is represented in a two-dimensional manner by the X-ray taken from just beside the face.
When the foregoing is considered, it will be said that a method of recording a state where the patient actually bites and a state where the jaws are opened by the thickness of the tooth positioner and reproducing the two types of states on the occluding apparatus is most accurate in order to know the relationship between the upper and lower jaws. The reason for this is that it is not so difficult for a skilled dentist to set the correct occlusion and opening positions of the patient in the mouth of the patient and make a recording of the relationship between the upper and lower jaws (hereinafter referred to as "bite"). In order to take a bite, a material which is mainly composed of silicon and is superior in operability and reproducibility is easily available.
However, it was infeasible from the following reasons to reproduce the two types of relationships between the upper and lower jaws at the time of occlusion and at the time of opening an occluding apparatus using two types of bites extracted from the patient.
In mounting the dentiform model on the occluding apparatus, there are currently a method of directly fastening upper and lower jaw teeth models, respectively, to portions, corresponding to the upper jaw and the lower jaw, of the occluding apparatus by gypsum and a method of fixing a dentiform model to the occluding apparatus using a magnet or a screw such that the dentiform model is detachable from the occluding apparatus as required. In the latter method, a mounting plate of a magnet type or a screw type or a so-called split cast is generally used. In producing the tooth positioner, the latter method in which the dentiform model is detachable from the occluding apparatus is suitable in terms of technical operations.
Consider a case where the relationships between the upper and lower jaws in two states, that is, a state where the respective sets of teeth of the upper and lower jaws are occluded and a state where they are opened by the thickness of the tooth positioner are reproduced on the occluding apparatus utilizing the two types of bites extracted in the mouth of the patient. In reproducing the two types of states on the occluding apparatus, it is considered that the upper jaw teeth model is mounted in the following two types of methods without changing the position where the lower jaw teeth model is mounted.
(1) Only two upper jaw teeth models which are the same are prepared, to respectively be mounted, using the bite extracted in the occluded state and the bite extracted in the opened state, the two states on an upper jaw portion of the occluding apparatus.
In this case, two types of blocks A and B for the upper jaw, including an upper jaw teeth model 4, are formed, as shown in FIGS. 3 (A) and 3 (B) (the A block reproduces the occluded state, and the B block reproduces the opened state). Accordingly, the two types of relationships between the upper and lower jaws can be reproduced by replacing the two blocks A and B with each other on an occluding apparatus 100.
Even if teeth of the dentiform model in the occluded state shown in FIG. 3 (A) are separated, and the separated teeth are newly rearranged, to make a set-up model, however, the set-up model cannot be brought into the state shown in FIG. 3 (B), that is, the opened state. Conversely, a set-up model cannot be produced from the dentiform model in the opened state shown in FIG. 3 (B). The reason for this is that the form of the teeth differs from patient to patient, so that the arrangement of the teeth in the occluded state cannot be presumed from the opened state, and the set-up model cannot be made from the dentiform model which is not in the occluded state.
(2) As another method, consider a method of reproducing the two types of relationships between the upper and lower jaws not using the two upper jaw teeth models but using a pair of upper and lower jaw teeth models. In this case, a state at the time of occlusion is obtained, in the same manner as that shown in FIG. 3 (A), as shown in FIG. 4 (A). However, an attempt to reproduce a state at the time of opening brings about the necessity of opening an upper jaw portion 5 of the occluding apparatus 100 itself, as shown in FIG. 4 (B).
The occluding apparatus 100 reproduces the motion of the jaw joints of a human being in approximate or average fashion, and does not faithfully reproduce the motion of the jaw joints of each patient, as described above. Even if an attempt to finely adjust the position where the A block is mounted with a bite 6 interposed between the lower jaw teeth model and the upper jaw teeth model is made in the state shown in FIG. 4 (B), the upper jaw teeth model 4 cannot be so adjusted as to fit the bite 6.
An attempt to make the adjustment brings about the necessity of further fastening the B block for correction on the A block.
In this case, even if the relationship between the upper and lower jaws at the time of opening can be reproduced, the B block for correction is fastened to the A block. In the A block A plus B block, therefore, the occluded state shown in FIG. 4 (A) cannot be reproduced even if the upper jaw portion 5 of the occluding apparatus 100 is lowered (closed).
As apparent from the foregoing consideration, in the method currently used, it is impossible to reproduce the two types of relationships between the upper and lower jaws which are required to produce the tooth positioner on the occluding apparatus.